Bacteria may be categorized into three fundamental groups based upon their growth relationship to oxygen: first, there are the aerobes which require oxygen for growth; second, there are the anaerobes which do not require the presence of oxygen for growth; and, third, there are the facultative anaerobes which have the capability for growing both in the presence of or in the absence of oxygen. With regard to the third group, however, facultative anaerobes derive more energy from nutrient materials aerobically than anaerobically and, consequently, develop more rapidly and to higher concentrations in the presence of oxygen rather than anaerobically.
One common method for obtaining large numbers of microorganisms for industrial use or for identification in clinical laboratories is to inoculate a specimen of the microorganisms into a liquid nutrient medium. If the microorganism is an aerobe, the oxygen level within the medium will become depleted within a relatively short period of time, thereby reducing further growth of the microorganism within the medium. Replenishment of the oxygen content in a liquid medium has customarily been accomplished in two ways: (1) by shaking the medium to provide a large surface area for gaseous exchange with the ambient air; or (2) by bubbling air or oxygen through the medium. Both methods have economic and practical shortcomings. Shaking demands space for large and expensive shaking equipment. Bubbling requires a source of compressed air or oxygen and hazards contamination of the culture by organisms entrained within the gas. As a natural consequence, then, many cultures are merely incubated in tubes with oxygen replenishment being dependent solely upon diffusion from the ambient air (Lennette, I. H., Spaulding, E. H., and Truant, J. P., Manual of Clinical Microbiology, 2nd Ed., American Society for Microbiology, 1974). It is obvious that the growth rates and total growth contents of such cultures will be severely limited when compared with fully aerated cultures. Yet, the time required for microbial growth constitutes a substantial proportion of the time employed in clinical microbiology services. It is believed evident that such services would be considerably improved if the time demanded for culture growth could be reduced significantly.
It is well known that oxygen is very soluble in certain silicone oils and fluorocarbon liquids. Thus, the solubility of oxygen in those liquids is many times greater than that in water. That characteristic of those materials has led to laboratory experiments wherein cats and mice have survived being immersed into such oxygen-saturated fluids for as long as several hours; air or oxygen being bubbled through the fluid (Golan, Frank, "Survival of Mammals Breathing Organic Fluids Equilibrated with Oxygen at Atmospheric Pressure," Science, 152, pp. 1755-6, June 24, 1966). As an extension of that work, those liquids have been brought into contact with solid and liquid nutrient media to accelerate the growth of microorganisms therein. That practice has indeed enhanced both the rate of growth and the level of growth of oxygen-utilizing microorganisms.
However, to insure air or oxygen-saturation of those fluids has required the above-mentioned shaking or bubbling techniques, both of which are cumbersome and economically unattractive. Therefore, the primary objective of this invention is to devise means for providing even larger amounts of air or oxygen than are soluble into those liquids, thereby making it possible to achieve even greater enhancement of aerobic and facultative anaerobic microorganism growth than that obtained via the use of the liquids alone. Also, this inventive means would not require shaking or bubbling to be effective.